661016domain: NAppears in sequencesNumber of cyclic arrangements (up to direction) of {0,1,...,n-1} such that the sum of any two neighbors is a prime.at n=18A242527a(n) is the sum of all integers of the form k^2 + 1 whose greatest prime factor is A002313(n), the n-th prime not congruent to 3 mod 4.at n=7A379347